Domain names or domain name extensions have been around for some time now. First we started off with .com which was the main domain extension used. Then, as the Internet grew, .net, .org were added along with .info and .biz. Now we have the all of the domain extensions below that are used by different companies and organizations.Some domain extensions are very popular like the .com but there are other domain extensions that never got off the ground. Please find below the list in alphabetical order of the main top level domain extensions. 

 Top Level Domains TLD Domain Names Extensions:

.aero Aviation
.arpa A top-level domain name used for ArpaNet sites.
.biz Business Organizations
.cat Catalan language and culture
.com A top-level domain name used for commercial Internet sites World-wide
.coop Co-Operative Organizations
.edu A top-level domain name used for educational sites in the United States
.firm An ending of an address for an Internet site for a business
.gov A top-level domain name used for a U.S. government site on the Internet
.info Open TLD
.int A top-level domain name used for international institutions
.jobs A top-level domain name for Jobs
.mil A top-level domain name for a U.S. military site on the Internet
.mobi A top-level domain name for a sites made for mobile phones
.museum A top-level domain name for Museums
.name A top-level domain name for Personal Names (not very popular now)
.nato A top-level domain name used for NATO sites
.net A top-level domain name used for Internet administrative sites in the United States
.org A top-level domain name for organizational Internet sites in the United States
.pro A top-level domain name for professionals
.store An ending of an address for an Internet site that is for a retail business
.travel A TLD for Travel related sites
.web An ending of an address for an Internet site that is about the World Wide Web